1. Field of the Invention
The present invention relates to method, apparatus and modulator configurations for electro-optically addressing (e.g. for imaging) high resolution picture elements (pixels). More specifically, the present invention relates to improved addressing electrode configurations and techniques for such electro-optic systems.
2. Description of Prior Art
U.S. Pat. No. 4,229,095 discloses various embodiments of electronic color-imaging apparatus that utilize arrays of separately-addressable, pixel (picture element) sized, electro-optical means to effect multicolor exposure of panchromatic imaging media. One preferred kind of electro-optical means disclosed in that patent is a light valve comprising a panel of ferroelectric ceramic material, such as lanthanum doped lead zirconate titanate (PLZT) sandwiched between crossed polarizers and activated to operate in a quadratic Kerr cell mode. Thus an array of such light valves comprises a panel of PLZT material with a plurality of interleaved electrodes formed on one major surface in a manner facilitating the selective application of discrete electrical fields across (in a direction perpendicular to the direction of viewing) discrete surface areas of the plate. Upon application of such fields, the PLZT material becomes birefringent and rotates the direction of polarization of incident light by an extent dependent on the field magnitude. This results in the transmission of light through the PLZT panel and polarizers varying as a function of the electric fields. A color image is formed electronically by selectively opening and closing such light valves in synchronization with the energization of red, green and blue exposing sources and according to the red, green and blue color information for the pixels of that image.
One difficult problem, which is presented in implementing address of such light valve arrays (and in the address of other analogous high resolution, electro-optic modulators), is to provide "efficient" electrode configurations for applying electrical potentials to create the desired electrical fields. From one viewpoint electrode configurations should be efficient as to minimizing modulator area which they occupy in order to maximize the area available for light modulation. From another viewpoint the electrode configurations should be efficient as to the number of terminals required to operatively connect them to the intended address control system. Also, it is desirable to minimize the number of switch and counter circuits needed to operate such modulator arrays, and electrode configuration often influences such switch and counter circuit requirements.
FIG. 2 illustrates one common kind of prior art electrode configuration for a high resolution electro-optic modulator 20. This configuration features a plurality of spaced reference-potential electrodes 21 that are commonly coupled and thus require only one connection terminal 23. Signal electrodes 22 are located respectively between reference electrode pairs and each have a separate terminal 24 to an address source, e.g. serial-in/parallel-out shift register 25. A high voltage switch (not shown) is required between each terminal 24 and the shift register 25. As shown, a signal potential "V" from the shift register turns its signal electrode 22 "on" and creates an activating field across pixel portion P.sub.1. A signal potential "0" leaves its signal electrode 22 off and pixel portion P.sub.2 thus remains "off". While this configuration is relatively efficient from the minimum-terminal viewpoint (i.e. it still requires one terminal and switch per pixel portion), it is not optically efficient, generally requiring two electrodes per pixel portion of the modulator.
FIG. 3 illustrates another prior art electrode configuration which is more efficient from the optical viewpoint, requiring one electrode per pixel portion. Thus modulator 30 has signal electrodes which are each independently addressable (via a terminal 34 and high-voltage switch, not shown) by a shift register 35. Data is input serially through an "exclusive or" gate so that adjacent signal electrodes 32 are of different potential if the pixel portion therebetween is to be "on" (e.g. P.sub.2 and P.sub.4) and at the same potential if the intermediate pixel portion is to be "off" (e.g. P.sub.1 and P.sub.3). This configuration still requires one terminal and switch (and perhaps counter) per pixel portion of the modulator. Further, it has been found that modulation efficiency of the FIG. 3 type configuration is sometimes reduced because the directions of the transverse electrical fields alter frequently according to demands of the group data input to the shift register.